1. Field of the Invention
The present invention relates to a communication system comprising a plurality of network elements and a monitoring apparatus for centrally monitoring and controlling these network elements. More particularly, the invention relates to techniques for performing file management and deterioration check in connection with the process of downloading software using an application entity (layer 7) of the OSI (Open System Interconnection).
2. Description of the Related Art
In a growing number of cases, network elements constituting a communication system are functionally updated today through software (program) updates. Software updates are easier to carry out than updates through hardware replacement in terms of debugging, functional reinforcement and expansion. But the ease of the software update scheme can result in its undoing. The easy-to-make updates may disable the entire communication system if not carried out correctly and scrupulously. To update successfully the software controlling the network elements requires adopting verification procedures demanding a lot of care and attention.
In a majority of communication systems comprising network elements such as optical terminal transmission devices interconnected via communication lines, the programs (firmware) for a plurality of CPU's (central processing units) are updated by maintenance personnel manually replacing ROM's (read only memories). Program versions are managed primarily through a ledger-based ROM version management scheme. From the time programs are stored into ROM's until the ROM contents are updated in the network elements, the programs in the ROM's are not electronically checked for validity.
As a result, it has happened that some of the programs in the ROM's having been destroyed or deteriorated were updated heedlessly and caused the network elements to malfunction. In other cases, the communication system was disrupted when ROM sockets were incorrectly reconnected. Furthermore, ROM replacement work has turned out to be a tedious and troublesome task.
To circumvent such disadvantages, a monitoring apparatus is connected via control lines to the network elements so that the latter are under centralized surveillance and control within the communication system. The programs executed by the CPU's in the network elements are transferred as download data from the monitoring apparatus to the network elements. The programs downloaded to the network elements are subject to CPU-wise program version management by the monitoring apparatus. The validity of the download data is ascertained by checking to see if the download data yet to be transferred coincides with the transferred download data. The checks are performed on the basis of the communication protocols established between the monitoring apparatus and the network elements.
In other words, the conventional version management of the programs transferred to the network elements involves having the monitoring apparatus check the versions of the programs for each of the CPU's. Such a management scheme is complicated and runs the risk of inadvertently transferring a combination of programs that are not functionally compatible. Checking the validity of the transferred download data simply involves confirming the coincidence between the yet-to-be transferred and the transferred download data. If any invalid program is inadvertently or maliciously transferred, the fault cannot be detected by the conventional scheme. Furthermore, there is a possibility that during or after the transfer of program files, part of the programs may be destroyed or degraded due to memory trouble or other hardware-related causes. Any of such contingencies can cripple the network elements and reduce the reliability of the communication system as a whole.